The present invention relates to a pattern or image recognition apparatus and, more particularly, to a pattern recognition apparatus for a drawing reader system, which involves tracing a pixel line of pixel line image data of an input drawing, converting into polygonal line data, shaping a minute shape portion of the polygonal line data, and reading the drawing.
In processing drawing data by digitizing a line drawing with drawing processing devices such as computer-aided design devices, a variety of shapes are extracted from the drawing in which various line segments are present and they are classified into drawing elements of lines. As a pre-processing of image processing at this time, the line drawing is read by a scanner or any other device and stored in a memory unit as pixel line image data of a pixel line image. Then the pixel line image data stored is subjected to polygonal line processing for converting the pixel line data into polygonal line data, thus approximating the drawing to a polygonal line by means of the polygonal line processing and classifying it into drawing elements.
The polygonal line processing for converting the pixel line image data into the polygonal line data is executed in order by three processing steps including a series of trace processing, polygonal line-converting processing and connection processing of polygonal lines. The trace processing of the pixel line is to form tracing pixel line image data by tracing each one of pixels of the pixel line and to conclude whether a branch point or a terminal point is detected. The polygonal-line converting processing is to form polygonal line data from the tracing pixel line image data for each of the pixel data traced. The connection processing is to connect each separate polygonal line data, thus processing into continuous polygonal line data and converting the pixel line image data into polygonal line data.
A shape of the drawing is then subjected to pattern recognition processing after conversion into the polygonal line data by means of the polygonal line processing. In this case, a shape of a curved portion of the polygonal line may be used as an important parameter for determining a shape of the drawing. However, it is to be noted that digital noise is likely to occur upon the polygonal line processing. Accordingly, the shaping processing is required for shaping a minute shape portion in the polygonal line processing.
A pattern recognition apparatus for recognizing the drawing is designed to implement the polygonal line processing by approximating a line image to a polygonal line and converted into the centerline dot line image data comprising an image line passing through the center of the line image. It is to be noted, however, that data which is obtained by approximation of the minute shape portion of the drawing to a polygonal line may in many instances be distorted or deviated in its shape. For example, if the polygonal line processing is implemented by taking advantage of the polygonal line approximation method (remotest dot method) which involves setting a data coordinate indicative of characteristics of a line image, digital noise may occur at its corner portion so that the recognition processing of a drawing pattern cannot be implemented with accuracy because no true drawing data is produced. In this respect, the shaping processing is required for shaping a minute shape portion of the polygonal line approximation after the polygonal line processing.
The shaping processing for shaping a minute shape portion may generally contain, for example, a technique of shaping polygonal line data statistically in a group taking such distortion into consideration. It is to be noted herein, however, that such shaping in a group statistically poses the problem of distinguishing such a distorted drawing from a drawing originally having a shape identical to or similar to such distortion.